The present invention relates to a multiband traveling wave tube capable of operating at high power. This tube, intended especially to be used in airborne and space applications, must be relatively short.
The development of techniques and the increasing control of materials have made it possible to develop traveling wave tubes intended to operate within a very wide frequency range and which are relatively short. These tubes are known as mini-TWTs. These are travelling wave tubes with a one-piece line in the form of a tight helix. From the frequency standpoint, a ratio of the high frequency to the low frequency of the band of at least 3 is obtained.
From the dimensional standpoint, these tubes do not exceed about thirty centimeters, but from the power standpoint they barely reach more than a few tens of watts.
It would be conceivable to extrapolate these tubes in order to increase their power but, for a given gain, achieving a higher power entails increasing the helix voltage and increasing its length. However, it is not a question of reducing the gain, so as to obtain the required power without increasing the length of the helix. This approach does not lead to a multiband traveling wave tube, of short length, capable of operating at high power.
The subject of the present invention is a multiband traveling wave tube which has a length of the order of that of a mini-TWT but which is capable of operating at higher powers, while still maintaining a gain of the same order of magnitude.
For this purpose, the multiband traveling wave tube according to the invention comprises a microwave line along which electrons travel and in which a signal is amplified. This microwave line comprises, in succession, a microwave line input section separated from a succession of gapped microwave line output sections, each output section working within one of the operating bands of the tube.
The input section is connected, at one end, to input means for injecting the signal to be amplified and works within a frequency band encompassing the operating frequency bands of the tube. It is intended to preamplify the signal to be amplified.
The succession of output sections receives the preamplified signal, each of its output sections being intended to amplify it if it is at a frequency lying within its working frequency band and to let it through virtually without any interaction if it is at a frequency outside its working frequency band, each of the output sections being connected at one end to output means for extracting the preamplified signal that it has amplified.
Preferably, the central frequencies of the working bands of the output sections decrease with their distance from the input section.
With regard to the power of the signal amplified by an output section, this increases the further the output section is from the input section.
The microwave line sections are in the form of a helix, each helix being held in place in a sheath by dielectric supports and the various sheaths being joined together.
To be able to work in a very wide band, the input section includes dispersion-correcting means, such as gates.
Preferably, the helix of the first output section will have substantially the same length and/or the same internal diameter as the helix of the input section.
The helical wire of the first output section will also preferably have the same cross section as that of the helical wire of the input section.
To maintain, in the first output section, the synchronism, acquired in the input section, between the velocity of the electron beam and the velocity of the signal, the pitch of the helix of the first output section will preferably be smaller than that of the helix of the input section.
Preferably, the length and/or the pitch and/or the internal diameter of the helices of the output sections will increase as they get further from the input section. The same applies to the cross section of the helical wire.
To avoid the appearance of self-oscillation phenomena, the input section is provided with an attenuation region at the opposite end to that connected to the means for injecting the signal to be amplified.
For this purpose, each output section is provided with an attenuation region at the opposite end to that connected to the means for extracting the signal that it has amplified.